Generally gear mechanisms, such as a trapezoidal thread worm gear mechanisms or a rack and pinion gear mechanisms, are used as the mechanism to convert rotary motion of an electric motor to an axial linear motion in an electric linear actuator. These actuators are used in various types of driving sections. These motion converting mechanisms involve sliding contact portions. Thus, power loss is increased. Accordingly, this necessitates an increase in the size of the electric motors and in power consumption. Accordingly, ball screw mechanisms have been widely adopted as more efficient actuators.
A prior art electric linear actuator is shown in FIG. 6. This electric linear actuator 50 includes an electric motor 51, a speed reduction mechanism 53, a gear casing 55, an end cover 56 and an intermediate cover 57. The speed reduction mechanism 53 reduces the rotational speed of the electric motor 51 and transmits it to an output shaft 52. The gear casing 55 contains the speed reduction mechanism 53. The gear casing 55 includes an opening 54 at one end side of the output shaft 52. The end cover 56 closes the opening 54 of the gear casing 55. The intermediate cover 57 is positioned between the gear casing 55 and the end cover 56 to bear one end of the output shaft 52. The speed reduction mechanism 53 is arranged on the gear casing 55 side with respect to the intermediate cover 57. A rotational position detecting device 58 is arranged on the end cover 56 side with respect to the intermediate cover 57.
The end cover 56 is fastened to the opening 54 of the gear casing 55. The entire periphery of the opening 54 of the gear casing 55 is formed with a groove 60. A packing 61 is arranged in the groove 60. The packing 61 prevents entry of dust or foreign matters into the inside of the speed reduction mechanism 53 through the junction between the gear casing 55 and the end cover 56. See, JP 2010-68559 A.
However, in the prior art sealing structures, the gear casing 55 and cover 56 are liable to be deformed since they are formed from material of low rigidity such as aluminum alloy. Thus, a gap or clearance caused by the deformation of the gear casing 55 or cover 56 cannot be sealed only by elastic deformation of the packing 61. Thus, the sealability of the speed reduction mechanism 53 cannot be assured.
In order to keep sealability of the electric linear actuator, liquid gasket with adhesiveness and viscosity is applied. Thus, it is an object of the present disclosure to provide an electric linear actuator with sealability between the joining surfaces of the housings.